Via Myron posting at Rontini's BBS, click here if you're ready to waste some time. I found out it is possible to get the sledder to make it around a loop, but he gets hung up inside of it. You can also make him crash headfirst into the mountain, thusly:
Update 0206 17 Oct: Actually, I found that by leaving a gap in the loop, you can make him go all the way around -- theoretically, at least. I've gotten the sled to go all the way through, but not with the sledder still aboard.